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Hyvärinen M, Huang Y, David E, Hynynen K. Comparison of computer simulations and clinical treatment results of magnetic resonance guided focused ultrasound surgery (MRgFUS) of uterine fibroids. Med Phys 2021; 49:2101-2119. [PMID: 34601729 PMCID: PMC9314069 DOI: 10.1002/mp.15263] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2021] [Revised: 08/31/2021] [Accepted: 08/31/2021] [Indexed: 11/15/2022] Open
Abstract
Purpose Magnetic resonance‐guided focused ultrasound surgery (MRgFUS) can be used to noninvasively treat symptomatic uterine fibroids by heating with focused ultrasound sonications while monitoring the temperature with magnetic resonance (MR) thermometry. While prior studies have compared focused ultrasound simulations to clinical results, studies involving uterine fibroids remain scarce. In our study, we perform such a comparison to assess the suitability of simulations for treatment planning. Methods Sonications (N = 67) were simulated retrospectively using acoustic and thermal models based on the Rayleigh integral and Pennes bioheat equation followed by MR‐thermometry simulation in seven patients who underwent MRgFUS treatment for uterine fibroids. The spatial accuracy of simulated focus location was assessed by evaluating displacements of the centers of mass of the thermal dose distributions between simulated and treatment MR thermometry slices. Temperature–time curves and sizes of 240 equivalent minutes at 43°C (240EM43) volumes between treatment and simulation were compared. Results The simulated focus location showed errors of 2.7 ± 4.1, −0.7 ± 2.0, and 1.3 ± 1.2 mm (mean ± SD) in the anterior–posterior, foot–head, and right–left directions for a fibroid absorption coefficient of 4.9 Np m–1 MHz–1 and perfusion parameter of 1.89 kg m–3 s–1. Linear regression of 240EM43 volumes of 67 sonications of patient treatments and simulations utilizing these parameters yielded a slope of 1.04 and a correlation coefficient of 0.54. The temperature rise ratio of simulation to treatment near the end of sonication was 0.47 ± 0.22, 1.28 ± 0.60, and 1.49 ± 0.71 for 66 sonications simulated utilizing fibroid absorption coefficient of 1.2, 4.9, and 8.6 Np m–1 MHz–1, respectively, and the aforementioned perfusion value. The impact of perfusion on peak temperature rise is minimal between 1.89 and 10 kg m–3 s–1, but became more substantial when utilizing a value of 100 kg m–3 s–1. Conclusions The results of this study suggest that perfusion, while in some cases having a substantial impact on thermal dose volumes, has less impact than ultrasound absorption for predicting peak temperature elevation at least when using perfusion parameter values up to 10 kg m–3 s–1 for this particular array geometry, frequencies, and tissue target which is good for clinicians to be aware of. The results suggest that simulations show promise in treatment planning, particularly in terms of spatial accuracy. However, in order to use simulations to predict temperature rise due to a sonication, knowledge of the patient‐specific tissue parameters, in particular the absorption coefficient is important. Currently, spatially varying patient‐specific tissue parameter values are not available during treatment, so simulations can only be used for planning purposes to estimate sonication performance on average.
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Affiliation(s)
- Mikko Hyvärinen
- Sunnybrook Research Institute, Toronto, Ontario, M4N 3M5, Canada.,Department of Medical Biophysics, University of Toronto, Toronto, Ontario, M5G 1L7, Canada
| | - Yuexi Huang
- Sunnybrook Research Institute, Toronto, Ontario, M4N 3M5, Canada
| | - Elizabeth David
- Sunnybrook Research Institute, Toronto, Ontario, M4N 3M5, Canada
| | - Kullervo Hynynen
- Sunnybrook Research Institute, Toronto, Ontario, M4N 3M5, Canada.,Department of Medical Biophysics, University of Toronto, Toronto, Ontario, M5G 1L7, Canada
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Dillon C, Rezvani M, McLean H, Adelman M, Dassel M, Jarboe E, Janát-Amsbury M, Payne A. A tissue preparation to characterize uterine fibroid tissue properties for thermal therapies. Med Phys 2019; 46:3344-3355. [PMID: 31152601 DOI: 10.1002/mp.13639] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2018] [Revised: 05/22/2019] [Accepted: 05/22/2019] [Indexed: 11/08/2022] Open
Abstract
PURPOSE Treating uterine fibroids with less invasive therapies such as magnetic resonance-guided focused ultrasound (MRgFUS) is an attractive alternative to surgery. Treatment planning can improve MRgFUS procedures and reduce treatment times, but the tissue properties that currently inform treatment planning tools are not adequate. This study aims to develop an ex vivo uterine fibroid model that can emulate the in vivo environment allowing for characterization of the uterus and fibroid MR, acoustic, and thermal tissue properties while maintaining viability for the necessary postsurgical histopathological assessments. METHODS Women undergoing a hysterectomy due to fibroid-related symptoms were invited to undergo a preoperative pelvic MRI and to permit postoperative testing of their uterine specimen. Patients that declined or could not be scheduled for a pre-operative MRI were still able to allow post-operative testing of their excised tissue. Following surgical removal of the uterus, nonmorcellated tissues were reperfused with a Krebs-Henseleit buffer solution. An MR-compatible perfusion system was designed to maintain tissue viability inside the MR suite during scanning. MR imaging protocols utilized preoperatively were repeated on whole sample, reperfused ex vivo uterus specimens. Thermal properties including thermal diffusivity and thermal conductivity of the uterus and fibroids were determined using an invasive needle sensor device in 50% of the specimens. Acoustic property measurements (density, speed of sound and attenuation) were obtained for approximately 20% of the tissue samples using both through-transmission and radiation force balance techniques. Differences between fibroid and uterus and in vivo and ex vivo measurements were evaluated with a two-tailed Student t test. RESULTS Fourteen patients participated in the study and measurements were obtained from 22 unique fibroids. Of the 16 fibroids available for preoperative MRI testing, 69% demonstrated classic hypo-intensity relative to the myometrium, with the remainder presenting with iso- (25%) or hyper-intensity (6%). While thermal diffusivity was not significantly different between fibroid and myometrium tissues (0.217 ± 0.047 and 0.204 ± 0.039 mm2 /s, respectively), the acoustic attenuation in fibroid tissue was significantly higher than myometrium (0.092 ± 0.021 and 0.052 ± 0.023 Np/cm/MHz, respectively). When comparing in vivo with ex vivo MRI T1 and T2 measurements in fibroids and myometrium tissue, the only difference was found in the fibroid T2 property (P < 0.05). Finally, the developed perfusion protocol successfully maintained tissue viability in ex vivo tissues as evaluated through histological analysis. CONCLUSIONS This study developed an MR-compatible extracorporeal perfusion technique that effectively maintains tissue viability, allowing for the direct measurement of patient-specific MR, thermal, and acoustic property values for both fibroid and myometrium tissues. These measured tissue property values will enable further development and validation of treatment planning models that can be utilized during MRgFUS uterine fibroid treatments.
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Affiliation(s)
- Christopher Dillon
- Department of Radiology and Imaging Sciences, University of Utah, Salt Lake City, UT, 84132, USA
| | - Maryam Rezvani
- Department of Radiology and Imaging Sciences, University of Utah, Salt Lake City, UT, 84132, USA
| | - Hailey McLean
- Department of Radiology and Imaging Sciences, University of Utah, Salt Lake City, UT, 84132, USA
| | - Marisa Adelman
- Department of Obstetrics and Gynecology, University of Utah, Salt Lake City, UT, 84132, USA
| | - Mark Dassel
- Department of Obstetrics and Gynecology, University of Utah, Salt Lake City, UT, 84132, USA
| | - Elke Jarboe
- Department of Obstetrics and Gynecology, University of Utah, Salt Lake City, UT, 84132, USA.,Department of Pathology, University of Utah, Salt Lake City, UT, 84112, USA
| | - Margit Janát-Amsbury
- Department of Obstetrics and Gynecology, University of Utah, Salt Lake City, UT, 84132, USA
| | - Allison Payne
- Department of Radiology and Imaging Sciences, University of Utah, Salt Lake City, UT, 84132, USA
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Rouyer J, Cueva T, Yamamoto T, Portal A, Lavarello RJ. In Vivo Estimation of Attenuation and Backscatter Coefficients From Human Thyroids. IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL 2016; 63:1253-1261. [PMID: 26955025 DOI: 10.1109/tuffc.2016.2532932] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Fine-needle aspiration (FNA) remains the gold standard for the diagnosis of thyroid cancer. However, currently, a large number of FNA biopsies result in negative or undetermined diagnosis, which suggests that better noninvasive tools are needed for the clinical management of thyroid cancer. Spectral-based quantitative ultrasound (QUS) characterizations may offer a better diagnostic management as previously demonstrated in mouse cancer models ex vivo. As a first step toward understanding the potential of QUS markers for thyroid disease management, this paper deals with the spectral-based QUS estimation of healthy human thyroids in vivo. Twenty volunteers were inspected by a trained radiologist using two ultrasonic imaging systems, which allowed them to acquire radio-frequency data spanning the 3-16-MHz frequency range. Estimates of attenuation coefficient slope (ACS) using the spectral logarithmic difference method had an average value of [Formula: see text]) with a standard deviation of [Formula: see text]. Estimates of backscatter coefficient (BSC) using the reference-phantom method had an average value of [Formula: see text] over the useful frequency range. The intersubject variability when estimating BSCs was less than 1.5 dB over the analysis frequency range. Further, the effectiveness of three scattering models (i.e., fluid sphere, Gaussian, and exponential form factors) when fitting the experimentally estimated BSCs was assessed. The exponential form factor was found to provide the best overall goodness of fit ( R2 = 0.917), followed by the Gaussian ( R2 = 0.807) and the fluid-sphere models ( R2 = 0.752). For all scattering models used in this study, average estimates of the effective scatterer diameter were between 44 and 56 μm. Overall, an excellent agreement in the estimated attenuation and BSCs with both scanners was exhibited.
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Nightingale KR, Church CC, Harris G, Wear KA, Bailey MR, Carson PL, Jiang H, Sandstrom KL, Szabo TL, Ziskin MC. Conditionally Increased Acoustic Pressures in Nonfetal Diagnostic Ultrasound Examinations Without Contrast Agents: A Preliminary Assessment. JOURNAL OF ULTRASOUND IN MEDICINE : OFFICIAL JOURNAL OF THE AMERICAN INSTITUTE OF ULTRASOUND IN MEDICINE 2015; 34:1-41. [PMID: 26112617 PMCID: PMC4822701 DOI: 10.7863/ultra.34.7.15.13.0001] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
The mechanical index (MI) has been used by the US Food and Drug Administration (FDA) since 1992 for regulatory decisions regarding the acoustic output of diagnostic ultrasound equipment. Its formula is based on predictions of acoustic cavitation under specific conditions. Since its implementation over 2 decades ago, new imaging modes have been developed that employ unique beam sequences exploiting higher-order acoustic phenomena, and, concurrently, studies of the bioeffects of ultrasound under a range of imaging scenarios have been conducted. In 2012, the American Institute of Ultrasound in Medicine Technical Standards Committee convened a working group of its Output Standards Subcommittee to examine and report on the potential risks and benefits of the use of conditionally increased acoustic pressures (CIP) under specific diagnostic imaging scenarios. The term "conditionally" is included to indicate that CIP would be considered on a per-patient basis for the duration required to obtain the necessary diagnostic information. This document is a result of that effort. In summary, a fundamental assumption in the MI calculation is the presence of a preexisting gas body. For tissues not known to contain preexisting gas bodies, based on theoretical predications and experimentally reported cavitation thresholds, we find this assumption to be invalid. We thus conclude that exceeding the recommended maximum MI level given in the FDA guidance could be warranted without concern for increased risk of cavitation in these tissues. However, there is limited literature assessing the potential clinical benefit of exceeding the MI guidelines in these tissues. The report proposes a 3-tiered approach for CIP that follows the model for employing elevated output in magnetic resonance imaging and concludes with summary recommendations to facilitate Institutional Review Board (IRB)-monitored clinical studies investigating CIP in specific tissues.
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Affiliation(s)
- Kathryn R Nightingale
- Department of Biomedical Engineering, Duke University, PO Box 90281, Durham, NC 27708 USA
| | - Charles C Church
- National Center for Physical Acoustics and Department of Physics and Astronomy, The University of Mississippi, University, MS 38677 USA
| | - Gerald Harris
- US Food and Drug Administration (Retired), Current Address: 132 S Van Buren St, Rockville, MD 20850 USA
| | - Keith A Wear
- US Food and Drug Administration, 10903 New Hampshire Ave, Building 62, Room 2104, Silver Spring, MD 20993-0002 USA
| | - Michael R Bailey
- Center for Industrial and Medical Ultrasound, Applied Physics Laboratory, University of Washington, 1013 NE 40th St, Seattle WA 98105 USA
| | - Paul L Carson
- Department of Radiology, University of Michigan Health System, 3218C Med Sci I, B Wing SPC 5667, Ann Arbor, MI 48109-5667 USA
| | - Hui Jiang
- Fujifilm SonoSite, 21919 30th Dr SE, Bothell, WA 98021 USA
| | - Kurt L Sandstrom
- Samsung Medison Co, Ltd, Building, 42, Teheran-ro, 108-gil, Gangnam-gu, Seoul 135-851, Korea
| | - Thomas L Szabo
- Department of Biomedical Engineering, Boston University, 44 Cummington Mall, Boston, MA 02215 USA
| | - Marvin C Ziskin
- Emeritus Professor of Radiology and Medical Physics, Temple University School of Medicine, Philadelphia, PA 19140 USA
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Wootton JH, Prakash P, Hsu ICJ, Diederich CJ. Implant strategies for endocervical and interstitial ultrasound hyperthermia adjunct to HDR brachytherapy for the treatment of cervical cancer. Phys Med Biol 2011; 56:3967-84. [PMID: 21666290 DOI: 10.1088/0031-9155/56/13/014] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Catheter-based ultrasound devices provide a method to deliver 3D conformable heating integrated with HDR brachytherapy delivery. Theoretical characterization of heating patterns was performed to identify implant strategies for these devices which can best be used to apply hyperthermia to cervical cancer. A constrained optimization-based hyperthermia treatment planning platform was used for the analysis. The proportion of tissue ≥41 °C in a hyperthermia treatment volume was maximized with constraints T(max) ≤ 47 °C, T(rectum) ≤ 41.5 °C, and T(bladder) ≤ 42.5 °C. Hyperthermia treatment was modeled for generalized implant configurations and complex configurations from a database of patients (n = 14) treated with HDR brachytherapy. Various combinations of endocervical (360° or 2 × 180° output; 6 mm OD) and interstitial (180°, 270°, or 360° output; 2.4 mm OD) applicators within catheter locations from brachytherapy implants were modeled, with perfusion constant (1 or 3 kg m(-3) s(-1)) or varying with location or temperature. Device positioning, sectoring, active length and aiming were empirically optimized to maximize thermal coverage. Conformable heating of appreciable volumes (>200 cm(3)) is possible using multiple sectored interstitial and endocervical ultrasound devices. The endocervical device can heat >41 °C to 4.6 cm diameter compared to 3.6 cm for the interstitial. Sectored applicators afford tight control of heating that is robust to perfusion changes in most regularly spaced configurations. T(90) in example patient cases was 40.5-42.7 °C (1.9-39.6 EM(43 °C)) at 1 kg m(-3) s(-1) with 10/14 patients ≥41 °C. Guidelines are presented for positioning of implant catheters during the initial surgery, selection of ultrasound applicator configurations, and tailored power schemes for achieving T(90) ≥ 41 °C in clinically practical implant configurations. Catheter-based ultrasound devices, when adhering to the guidelines, show potential to generate conformal therapeutic heating ranging from a single endocervical device targeting small volumes local to the cervix (<2 cm radial) to a combination of a 2 × 180° endocervical and directional interstitial applicators in the lateral periphery to target much larger volumes (6 cm radial), while preferentially limiting heating of the bladder and rectum.
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Affiliation(s)
- Jeffery H Wootton
- Department of Radiation Oncology, University of California, San Francisco, CA 94115, USA
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Wootton JH, Hsu ICJ, Diederich CJ. Endocervical ultrasound applicator for integrated hyperthermia and HDR brachytherapy in the treatment of locally advanced cervical carcinoma. Med Phys 2011; 38:598-611. [PMID: 21452697 DOI: 10.1118/1.3512803] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
PURPOSE The clinical success of hyperthermia adjunct to radiotherapy depends on adequate temperature elevation in the tumor with minimal temperature rise in organs at risk. Existing technologies for thermal treatment of the cervix have limited spatial control or rapid energy falloff. The objective of this work is to develop an endocervical applicator using a linear array of multisectored tubular ultrasound transducers to provide 3-D conformal, locally targeted hyperthermia concomitant to radiotherapy in the uterine cervix. The catheter-based device is integrated within a HDR brachytherapy applicator to facilitate sequential and potentially simultaneous heat and radiation delivery. METHODS Treatment planning images from 35 patients who underwent HDR brachytherapy for locally advanced cervical cancer were inspected to assess the dimensions of radiation clinical target volumes (CTVs) and gross tumor volumes (GTVs) surrounding the cervix and the proximity of organs at risk. Biothermal simulation was used to identify applicator and catheter material parameters to adequately heat the cervix with minimal thermal dose accumulation in nontargeted structures. A family of ultrasound applicators was fabricated with two to three tubular transducers operating at 6.6-7.4 MHz that are unsectored (360 degrees), bisectored (2 x 180 degrees), or trisectored (3 x 120 degrees) for control of energy deposition in angle and along the device length in order to satisfy anatomical constraints. The device is housed in a 6 mm diameter PET catheter with cooling water flow for endocervical implantation. Devices were characterized by measuring acoustic efficiencies, rotational acoustic intensity distributions, and rotational temperature distributions in phantom. RESULTS The CTV in HDR brachytherapy plans extends 20.5 +/- 5.0 mm from the endocervical tandem with the rectum and bladder typically <8 mm from the target boundary. The GTV extends 19.4 +/- 7.3 mm from the tandem. Simulations indicate that for 60 min treatments the applicator can heat to 41 degrees C and deliver > 5EM(43 degrees C) over 4-5 cm diameter with Tmax < 45 degrees C and 1 kg m(-3) s(-1) blood perfusion. The 41 degrees C contour diameter is reduced to 3-4 cm at 3 kg m(-3) s(-1) perfusion. Differential power control to transducer elements and sectors demonstrates tailoring of heating along the device length and in angle. Sector cuts are associated with a 14-47 degrees acoustic dead zone, depending on cut width, resulting in a approximately 2-4 degrees C temperature reduction within the dead zone below Tmax. Dead zones can be oriented for thermal protection of the rectum and bladder. Fabricated devices have acoustic efficiencies of 33.4%-51.8% with acoustic output that is well collimated in length, reflects the sectoring strategy, and is strongly correlated with temperature distributions. CONCLUSIONS A catheter-based ultrasound applicator was developed for endocervical implantation with locally targeted, 3-D conformal thermal delivery to the uterine cervix. Feasibility of heating clinically relevant target volumes was demonstrated with power control along the device length and in angle to treat the cervix with minimal thermal dose delivery to the rectum and bladder.
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Affiliation(s)
- Jeffery H Wootton
- Thermal Therapy Research Group, Department of Radiation Oncology, University of California, San Francisco, California 94115, USA
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Held RT, Zderic V, Nguyen TN, Vaezy S. Annular phased-array high-intensity focused ultrasound device for image-guided therapy of uterine fibroids. IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL 2006; 53:335-48. [PMID: 16529108 DOI: 10.1109/tuffc.2006.1593372] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
An ultrasound (US), image-guided high-intensity focused ultrasound (HIFU) device was developed for noninvasive ablation of uterine fibroids. The HIFU device was an annular phased array, with a focal depth range of 30-60 mm, a natural focus of 50 mm, and a resonant frequency of 3 MHz. The in-house control software was developed to operate the HIFU electronics drive system for inducing tissue coagulation at different distances from the array. A novel imaging algorithm was developed to minimize the HIFU-induced noise in the US images. The device was able to produce lesions in bovine serum albumin-embedded polyacrylamide gels and excised pig liver. The lesions could be seen on the US images as hyperechoic regions. Depths ranging from 30 to 60 mm were sonicated at acoustic intensities of 4100 and 6100 W/cm2 for 15 s each, with the latter producing average lesion volumes at least 63% larger than the former. Tissue sonication patterns that began distal to the transducer produced longer lesions than those that began proximally. The variation in lesion dimensions indicates the possible development of HIFU protocols that increase HIFU throughput and shorten tumor treatment times.
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Affiliation(s)
- Robert Thomas Held
- Center for Industrial and Medical Ultrasound, Applied Physics Laboratory, University of Washington, Seattle, WA, USA.
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Bigelow TA, O'Brien WD. A model for estimating ultrasound attenuation along the propagation path to the fetus from backscattered waveforms. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2005; 118:1210-20. [PMID: 16158675 PMCID: PMC2404117 DOI: 10.1121/1.1945564] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Accurate estimates of the ultrasound pressure and/or intensity incident on the developing fetus on a patient-specific basis could improve the diagnostic potential of medical ultrasound by allowing the clinician to increase the transmit power while still avoiding the potential for harmful bioeffects. Neglecting nonlinear effects, the pressure/intensity can be estimated if an accurate estimate of the attenuation along the propagation path (i.e., total attenuation) can be obtained. Herein, a method for determining the total attenuation from the backscattered power spectrum from the developing fetus is proposed. The boundaries between amnion and either the fetus' skull or soft tissue are each modeled as planar impedance boundaries at an unknown orientation with respect to the sound beam. A mathematical analysis demonstrates that the normalized returned voltage spectrum from this model is independent of the planes orientation. Hence, the total attenuation can be estimated by comparing the location of the spectral peak in the reflection from the fetus to the location of the spectral peak in a reflection obtained from a rigid plane in a water bath. The independence of the attenuation estimate and plane orientation is then demonstrated experimentally using a Plexiglas plate, a rat's skull, and a tissue-mimicking phantom.
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Affiliation(s)
- Timothy A Bigelow
- Bioacoustics Research Laboratory, Department of Electrical and Computer Engineering, University of Illinois, 405 North Mathews, Urbana, Illinois 61801, USA.
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Chan AH, Fujimoto VY, Moore DE, Martin RW, Vaezy S. An image-guided high intensity focused ultrasound device for uterine fibroids treatment. Med Phys 2002; 29:2611-20. [PMID: 12462728 DOI: 10.1118/1.1513990] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
A high intensity focused ultrasound (HIFU) device was developed for treating uterine fibroid tumors. This prototype device enables image-guided therapy by aligning a commercially available abdominal ultrasound image probe to a vaginal HIFU transducer so the HIFU focus is in the image plane. The device was designed based on anatomical constraints of the female pelvic structures. HIFU was generated using a 3.5 MHz PZT-8 crystal, 25.4 mm in diameter, bonded to an aluminum lens. Computer simulations were performed to ensure that effective focusing was achievable at a fixed focal depth of 40 mm. Transducer efficiency was empirically determined to be 58%, and the half pressure maximum focal dimensions were 11 mm in length and 1.2 mm in width. A water-filled latex condom surrounding the transducer provided acoustic coupling, a stand-off, and allowed water circulation for transducer cooling. In vitro experiments in a tissue-mimicking gel phantom and in turkey breast demonstrated ultrasound image-guided lesion formation, or tissue necrosis, at the focus due to HIFU induced thermal and cavitation effects. The HIFU treatment site appeared as a hyperechoic spot on the ultrasound image at intensities above 1250 W/cm2. The results of in vitro experiments and in vivo ergonomic testing in six human volunteers indicated that the device has the potential of providing a nonsurgical approach for uterine fibroid treatment. Future in vivo studies in large animal models and fibroids patients are planned.
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Affiliation(s)
- Arthur H Chan
- Department of Bioengineering, University of Washington, Seattle, Washington 98105, USA.
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